The present invention relates to an apparatus for continuously producing a precipitate by reacting together at least two reactants. More specifically, the invention relates to a vortex apparatus, intended more particularly for producing precipitates which are particularly adhesive during their formation.
A precipitation apparatus is already known, which comprises a fixed cylindrical vessel having a vertical axis into which the reagents are continuously introduced at the top of the said vessel and in the vicinity of its axis. A stirrer formed by a magnetized bar is positioned on the bottom of the vessel. The rotation of this bar is controlled by a rotary magnetic field generator positioned below the bottom of the vessel. The rotation of the stirrer makes it possible to produce a vortex, which has the effect of stirring the mixture and removing the freshly formed precipitates from the walls. Thus, the precipitates, which are denser than the solution, form in the vicinity of the vessel axis and tend to become localized there. Thus, the precipitates age in the vicinity of the vessel axis before lightly touching the vessel walls and are discharged with the solution via an overflow formed in the upper part of the vessel. Heating means may have to be provided outside the vessel if made necessary by the chemical reaction.
Thus, in this known apparatus, the vortex has the effect of moving the freshly formed precipitates away from the supports, which prevents incrustation of the apparatus when the precipitates are particularly adhesive. However, this apparatus has a certain number of disadvantages. Thus, when the envisaged chemical reaction involves radioactive products, the limits imposed by the safety conditions significantly restrict the capacity of such an apparatus. The increase in the capacity consequently necessitates the arrangement in parallel of a plurality of such apparatus, which has the effect of complicating the division of the feeds and the collection from the overflows. Moreover, the friction of the stirrer on the bottom of the vessel leads to a relatively short service life of the apparatus, which can only be improved by equipping the stirrer and the bottom of the vessel with special coatings based on tetrafluoroethylene and stainless steel. The effect of such equipment is to significantly increase the cost of the precipitator and leads to a limited period of use. In addition, the direct discharge of the precipitate through an overflow formed in the fixed vessel is accompanied by a simultaneous discharge of the solution, which is explained by the fact that the precipitates are denser than the solution.
In addition, precipitation apparatus are known, which comprise two, coaxial, fixed, cylindrical channels having vertical axes into which the reagents are introduced via the upper part of the central channel. The mixture is stirred by means of a plurality of stirrers regularly distributed around a rotary shaft positioned in the central channel. The rotary shaft carries a bladed turbine beneath the lower orifice of the central tube. This turbine ensures the raising of the precipitate and the solution in the lateral channel up to an overflow provided in the upper part of the lateral channel. This apparatus functions discontinuously, because the velocity of the liquids in the lateral outlet channel would be too low to raise the precipitate up to the overflow. This would lead to the choking up of the apparatus. Moreover, the precipitates tend to form dense beds between the stirrers.
Finally, precipitation apparatus are known, which comprise two fixed, coaxial, cylindrical channels in which the mixture is stirred by means of a scraper, which rotates in the central channel and undergoes vertical shocks to ensure its cleaning. At the bottom of the central channel, the reagents are stirred by a turbine, which localizes a dense precipitate bed. The solution rises in the lateral channel and is then discharged through an overflow. During its rise, the solution is purified of the precipitate, which settles and passes through the dense bed to be received at the base of the apparatus. Although this apparatus functions continuously, it does not permit a very high flow rate, because the increase in the flow rate helps to bring about the incrustation of the scraper. Moreover, in this solution, the precipitate must be raised at the outlet of the apparatus and it should be noted that the increase in the flow rate is also unfavourable to the raising of the precipitate.